768 Dr. A. N. Lucian on the Distribution of the 



was exposed. Curves were plotted for each pressure and 

 from these the distance #, in which the activity fell to half- 

 value, was measured and the velocity v calculated, taking 

 the half-value time to be 3*9 sees. It must be remembered 

 that these determinations of velocity for a given pressure are 

 not absolute, and that any change in the resistance of the 

 line will change the velocity of the flow. This was noticed 

 constantly during the course of the investigation. 



The pressure of the air current finally chosen was about 

 14'0 cm. of H 2 S0 4 . With this pressure the velocity obtained 

 was about 5 mm. per sec, and the concentration of the 

 emanation fell to less than one per cent, in a distance of 

 about 15 cm., which is more than one-half the height of the 

 vessel employed. It will be seen that with this velocity 

 more than one-half of the emanation would be found above 

 the first few mms. of the central electrode, the only places- 

 where any irregularities may be expected. Thus the velocity 

 chosen gives us a fair degree of approximation to the ideal 

 case where the emanation may be uniformly distributed in 

 the vessel and the deposit made evenly along the length of 

 the electrodes. 



As is to be expected, experiments with lower pressures-,, 

 such as 9 cm. and 5 cm. of H 2 S0 4 , gave smaller values of 

 the percentage of cathode activity, due to edge-effect and 

 other causes which helped the case to get more than its share 

 of the activity. 



Mention might be made here of one or two experiments in 

 which it was found that the distribution of the activity was 

 perceptibly affected (the cathode percentage activity being- 

 increased) in the case where the flow was asymmetrical with 

 respect to the central electrode, three out of four outlet tubes 

 being stopped. 



The effect of the irregularities of the field was examined 

 in a separate series of experiments. The variation of the 

 electric intensity in the cylindrical portion of the vessel and 

 in the bottom will not obey the same law, no matter what the 

 construction of the bottom is. As a consequence, we would 

 expect to find discrepancies in the relative number of the 

 neutral particles formed in the body of the vessel and near 

 the bottom, and diffusing to the electrodes. The bottom 

 corner of the vessel was filled in with a curved piece to get 

 rid of the edge effect, and gauze bottoms of various shapes, 

 flat and curved, tried. It was then found that, although 

 discrepancies in the values of the cathode percentage for 

 different shaped gauzes occurred, these never exceeded 

 the limits of experimental error, and did not exhibit any 



